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United States Patent |
5,645,958
|
Zhang
,   et al.
|
July 8, 1997
|
Superabsorbent polymer electrolytes for electrochemical cells and
electrochemical cells using same
Abstract
An electrolyte system 40 for use in connection with an electrochemical cell
(10). The cell (10) includes a positive (20) and a negative (30)
electrode, and the electrolyte system (40) disposed there between. The
electrolyte system includes a liquid electrolyte adapted to provide ion
transport between the positive and negative electrodes and a polymeric
support structure for engaging the liquid electrolyte.
Inventors:
|
Zhang; Jinshan (Coral Springs, FL);
Venugopal; Ganesh (Plantation, FL)
|
Assignee:
|
Motorola, Inc. (Schaumburg, IL)
|
Appl. No.:
|
251066 |
Filed:
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May 31, 1994 |
Current U.S. Class: |
429/337; 429/338; 429/339; 429/340; 429/341 |
Intern'l Class: |
H01M 006/18 |
Field of Search: |
429/192,213,249,254
|
References Cited
U.S. Patent Documents
4814242 | Mar., 1989 | Maxfield et al. | 429/217.
|
4987157 | Jan., 1991 | Smart et al. | 521/50.
|
5075399 | Dec., 1991 | Ahmed et al. | 526/287.
|
5098970 | Mar., 1992 | Hsieh et al. | 526/287.
|
5106929 | Apr., 1992 | Ahmed et al. | 526/240.
|
5130389 | Jul., 1992 | Ahmed et al. | 526/240.
|
5130391 | Jul., 1992 | Ahmed et al. | 526/288.
|
5196278 | Mar., 1993 | Idota | 429/194.
|
5252690 | Oct., 1993 | Ahmed et al. | 526/258.
|
Primary Examiner: Gorgos; Kathryn
Attorney, Agent or Firm: Massaroni; Kenneth M.
Claims
What is claimed is:
1. An electrolyte system for use in an electrochemical cell having positive
and negative electrodes, said system comprising:
an electrochemically active material which promotes ion transport between
said positive and said negative electrodes; and
an organic support structure fabricated of a superabsorbent polymer
material, said support structure holding in excess of 200 weight percent
of said electrochemically active material wherein the superabsorbent
polymer is of a crosslinked biphenyl-based polymer.
2. An electrolyte system as in claim 1, wherein said electrochemically
active material is a liquid electrolyte, and said support structure
absorbs said electrolyte.
3. An electrolyte system as in claim 2, wherein said liquid electrolyte is
an alkali metal salt dissolved in a non-protonic organic solvent.
4. An electrolyte system as in claim 3, wherein said alkali metal salt is
selected from the group consisting of materials having the formula M.sup.+
X.sup.- where:
M.sup.+ is an alkali metal cation selected from the group consisting of
Li.sup.+, Na.sup.+, and K.sup.+, and
X.sup.- is an anion selected from the group consisting of Cl.sup.-,
Br.sup.-, I.sup.-, ClO.sub.4.sup.-, BF.sub.4.sup.-, PF.sub.5.sup.-,
AsF.sub.6.sup.-, SbF.sub.6.sup.-, CH.sub.3 CO.sub.2.sup.-, CF.sub.3
SO.sub.3.sup.-, (CF.sub.3 SO.sub.2).sub.2 N.sub.2.sup.-, (CF.sub.3
SO.sub.2).sub.3 C.sup.-, and combinations thereof.
5. An electrolyte system as in claim 3, wherein said nonprotonic organic
solvent is selected from the group consisting of propylene carbonate,
ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl
carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane,
diethoxyethane, tetrahydrofuran, and combinations thereof.
6. An electrolyte system as in claim 3, wherein said electrochemically
active material is LiClO.sub.4 in propylene carbonate.
7. An electrolyte system as in claim 1, further including a binder
material.
8. An electrolyte system as in claim 7, wherein said binder material is
selected from the group consisting of poly(ethylene oxide),
poly(isobutylene), poly(butyldiene), poly(vinyl alcohol), poly(ethylene),
poly(propylene), poly(vinylidene fluoride), poly(dimethylsiloxene),
poly(acrylonitrile), ethylene-propylene-diene-monomer,
acrylonytrile-butyldiene, rubber tetra(ethylene glycol) diacrylate and
combinations thereof.
9. An electrolyte system as in claim 8, wherein said binder material is
poly(ethylene oxide).
10. An electrolyte system as in claim 11, wherein said binder material is
poly(isobutylene).
11. An electrolyte system as in claim 1, wherein said superabsorbent
polymer support structure is fabricated of a material having repeating
units selected from the group consisting of 1,4-phenylene,
4,4'-biphenylene, 4,4"-p-terphenylene, 1,3,5-phenylene, and combinations
thereof.
12. An electrolyte system as in claim 11, wherein said superabsorbent
polymer support structure is fabricated from 4,4'-biphenylene polymeric
network comprising tris(4,4'-biphenylene) carbinol repeating units.
13. An electrolyte system for use in an electrochemical cell, said system
including an electrochemically active material, and a superabsorbent
support structure characterized by ionic conductivity in excess of
3.0.times.10.sup.-3 S/cm, surface areas in excess of 100 m.sup.2 /g, and
porosity in excess of 20% wherein the superabsorbent polymer is of a
crosslinked biphenyl-based polymer.
14. An electrolyte system as in claim 13, wherein said electrochemically
active material is a liquid electrolyte, and said support structure
absorbs said electrolyte.
15. An electrolyte system as in claim 14, wherein said liquid electrolyte
is an alkali metal salt dissolved in a non-protonic organic solvent.
16. An electrolyte system as in claim 15, wherein said alkali metal salt is
selected from the group consisting of materials having the formula
M+X.sup.- where:
M.sup.+ is an alkali metal cation selected from the group consisting of
Li.sup.+, Na.sup.+, K.sup.+, and
X.sup.- is an anion selected from the group consisting of Cl.sup.-,
Br.sup.-, I.sup.-, ClO.sub.4.sup.-, BF.sub.4.sup.-, PF.sub.5.sup.-,
AsF.sub.6.sup.-, SbF.sub.6.sup.-, CH.sub.3 CO.sub.2.sup.-, CF.sub.3
SO.sub.3.sup.-, (CF.sub.3 SO.sub.2).sub.2 N.sub.2.sup.-, (CF.sub.3
SO.sub.2).sub.3 C.sup.-, and combinations thereof.
17. An electrolyte system as in claim 15, wherein said nonprotonic organic
solvents are selected from the group consisting of propylene carbonate,
ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl
carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane,
diethoxyethane, tetrahydrofuran, and combinations thereof.
18. An electrolyte system as in claim 15, wherein said electrochemically
active material is LiClO.sub.4 in propylene carbonate.
19. An electrolyte system as in claim 13, further including a binder
material.
20. An electrolyte system as in claim 19, wherein said binder material is
selected from the group consisting of poly(ethylene oxide),
poly(isobutylene), poly(butyldiene), poly(vinyl alcohol), poly(ethylene),
poly(propylene), poly(vinylidene fluoride), poly(dimethylsiloxene),
poly(acrylonitrile, ethylene-propylene-diene-monomer,
acrylonytrilebutyldiene rubber, tetra(ethylene glycol) diacrylate and
combinations thereof.
21. An electrolyte system as in claim 20, wherein said binder material is
poly(ethylene oxide).
22. An electrolyte system as in claim 20, wherein said binder material is
poly(isobutylene).
23. An electrolyte system as in claim 13, wherein said superabsorbent
support structure is fabricated of a material having repeating units
selected from the group consisting of 1,4-phenylene, 4,4'-biphenylene,
4,4"-p-terphenylene, 1,3,5-phenylene, and combinations thereof.
24. An electrolyte system as in claim 23, wherein said support structure is
fabricated from a crosslinked 4,4'-biphenylene polymer network comprising
tris(4,4'-biphenylene) carbinol repeating units.
25. An electrochemical cell comprising:
a positive electrode;
a negative electrode; and
an electrolyte system comprising a liquid electrolyte absorbed into a
superabsorbent polymer support structure.
26. An electrochemical cell as in claim 25, wherein said electrolyte system
further includes a binder material.
27. An electrolyte system as in claim 26, wherein said binder material is
selected from the group consisting of poly(ethylene oxide),
poly(isobutylene), poly(butyldiene), poly(vinyl alcohol), poly(ethylene),
poly(propylene), poly(vinylidene fluoride), poly(dimethylsiloxene),
poly(acrylonitrile) ethylene-propylene-diene-monomer,
acrylonytrile-butyldiene rubber, tetra(ethylene glycol) diacrylate and
combinations thereof.
28. An electrochemical cell as in claim 27, wherein said binder material is
poly(ethylene oxide).
29. An electrochemical cell as in claim 27 wherein said binder material is
poly(isobutylene).
30. An electrochemical cell as in claim 25, wherein said support structure
is fabricated of a material having repeating units selected from the group
consisting of 1,4-phenylene, 4,4'-biphenylene, 4,4"-p-terphenylene,
1,3,5-phenylene, and combinations thereof.
31. An electrochemical cell as in claim 30, wherein said support structure
is fabricated from a crosslinked 4,4'-biphenylene polymer network
comprising tris (4,4'-biphenylene) carbinol repeating units.
32. An electrochemical cell as in claim 25, wherein said liquid electrolyte
is an alkali metal salt dissolved in a non-protonic organic solvent.
33. An electrolyte system as in claim 32, wherein said alkali metal salt is
selected from the group consisting of materials having the formula M.sup.+
X.sup.- where:
M.sup.+ is an alkali metal cation selected from the group consisting of
Li.sup.+, and Na.sup.+, K.sup.+, and
X- is an anion selected from the group consisting of Cl.sup.-, Br.sup.-,
I.sup.-, ClO.sub.4.sup.-, BF.sub.4.sup.-, PF.sub.5.sup.-, AsF.sub.6.sup.-,
SbF.sub.6.sup.-, CH.sub.3 CO.sub.2.sup.-, CF.sub.3 SO.sub.3.sup.-,
(CF.sub.3 SO.sub.2).sub.2 N.sub.2.sup.-, (CF.sub.3 SO.sub.2).sub.3
C.sup.-, and combinations thereof.
34. An electrochemical cell as in claim 32, wherein said nonprotonic
organic solvents are selected from the group consisting of propylene
carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate,
dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane,
diethoxyethane, tetrahydrofuran, and combinations thereof.
35. An electrochemical cell as in claim 32, wherein said electrochemically
active material is LiClO.sub.4 in propylene carbonate.
Description
TECHNICAL FIELD
This invention relates in general to the field of electrolytes for
electrochemical cells, and more particularly to polymer electrolytes for
such cells.
BACKGROUND
There has been a great deal of interest in developing better and more
efficient methods for storing energy for applications such as radio
communication, satellites, portable computers, and electric vehicles to
name but a few. Accordingly, there have been recent concerted efforts to
develop high energy, cost effective batteries having improved performance
characteristics.
Rechargeable, or secondary cells are more desirable than primary
(non-rechargeable) cells since the associated chemical reactions which
take place at the positive and negative electrodes of the battery are
reversible. Electrodes for secondary cells are capable of being
regenerated (i.e. recharged) many times by the application of an
electrical charge thereto. Numerous advanced electrode systems have been
developed for storing electrical charge. Concurrently, much effort has
been dedicated to the development of electrolytes capable of enhancing the
capabilities of electrochemical cells.
Heretofore, electrolytes have been either liquid electrolytes as are found
in conventional wet cell batteries, or solid films as are available in
newer, more advanced battery systems. Each of these systems have inherent
limitations, and related deficiencies which make them unsuitable for
various applications.
Liquid electrolytes, while demonstrating acceptable ionic conductivity,
tend to leak out of the cells into which they are sealed. While better
manufacturing techniques have lessened the occurrence of leakage, cells
still do leak potentially dangerous liquid electrolytes from time to time.
This is particularly true of current lithium ion cells. Moreover, any
leakage in the cell lessens the amount of electrolyte available in the
cell, thus reducing the effectiveness of the cell. Cells using liquid
electrolytes are also not available for all sizes and shapes of batteries.
Conversely, solid electrolytes are free from problems of leakage. However,
they have vastly inferior properties as compared to liquid electrolytes.
For example, conventional solid electrolytes have ionic conductivities in
the range of 10.sup.-5 S/cm. Whereas acceptable ionic conductivity is
>10.sup.-3 S/cm. Good ionic conductivity is necessary to ensure a battery
system capable of delivering usable amounts of power for a given
application. Good conductivity is necessary for the high rate operation
demanded by, for example, cellular telephones and satellites. Accordingly,
solid electrolytes are not adequate for many high performance battery
systems.
One solution which has been proposed relates to the use of so-called gel
electrolytes for electrochemical systems. These types of electrolytes have
not been entirely successful as they tend to dissolve in the electrolyte
solvent, thus losing mechanical integrity.
Accordingly, there exists a need for a new electrolyte system which
combines the mechanical stability and freedom from leakage offered by
solid electrolytes with the high ionic conductivities of liquid
electrolytes.
SUMMARY OF THE INVENTION
Briefly, according to the invention, there is provided an electrolyte
system for use in an electrochemical cell having positive and negative
electrodes. The electrolyte system includes an electrochemically active
material or species, such as a liquid electrolyte, adapted to promote ion
transport between the positive and negative electrodes. The electrolyte
system further includes an organic support structure fabricated of a
polymeric material. The polymeric material is adapted to engage, as by
absorption, in excess of 200 weight % of the electrochemically active
material.
Further, according to an alternate embodiment of the invention, there is
provided an electrochemical cell including a positive and negative
electrode and an electrolyte system. The electrolyte system comprises an
electrochemically active material or species, such as a liquid
electrolyte, and a superabsorbent organic support structure for absorbing
said electrochemically active species.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representative of an electrochemical cell in
accordance with the instant invention;
FIG. 2 is an AC impedance spectrum of an electrolyte system in accordance
with the instant invention;
FIG. 3 is an AC impedance spectrum for an alternate embodiment of an
electrolyte system in accordance with instant invention.
FIG. 4 is an AC impedance spectrum for another alternate embodiment of an
electrolyte system in accordance with the instant invention.
FIG. 5 is an AC impedance spectrum for another alternate embodiment of an
electrolyte system in accordance with the instant invention;
FIG. 6 is an AC impedance spectrum for an alternate embodiment of an
electrolyte system in accordance with the instant invention; and
FIG. 7 is a cyclic voltammagram for an electrolyte system in accordance
with the instant invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
While the specification concludes with claims defining the features of the
invention that are regarded as novel, it is believed that the invention
will be better understood from a consideration of the following
description in conjunction with the drawing figures, in which like
reference numerals are carried forward.
Referring now to FIG. 1, there is illustrated therein a schematic
representation of an electrochemical cell in accordance with the instant
invention. The cell 10 includes a positive electrode 20 and a negative
electrode 30. The positive electrode 20 may be fabricated of any of a
number of chemical systems known to those of ordinary skill in the art.
Examples of such systems include manganese oxide, nickel oxide, cobalt
oxide, vanadium oxide, and combinations thereof. The negative electrode 30
may likewise be fabricated from any of a number of electrode materials
known to those of ordinary skill in the art. Selection of the negative
electrode material is dependent on the selection of the positive electrode
so as to assure an electrochemical cell which will function properly for a
given application. In this context, the negative electrode may be
fabricated from alkali metals, alkali metal alloys, carbon, graphite,
petroleum coke, and combinations thereof.
Operatively, disposed between the positive 20 and negative 30 electrodes is
an electrolyte system 40. The electrolyte system 40 comprises an organic
polymeric support structure adapted to engage, as for example, by
absorption, in excess 200 wt % and up to or in excess of 500 wt % of an
electrochemically active species or material. The electrochemically active
material may be a liquid electrolyte adapted to promote ion transport
between said positive 20 and negative 30 electrodes.
The liquid electrolyte absorbed by the organic support structure is
selected to optimize performance of the positive 20 and negative 30
electrode couple. The liquid electrolyte absorbed by the organic support
structure is, therefore, typically a solution of an alkali metal salt, or
combination of salts, dissolved in a non-protonic organic solvent or
solvents. Typical alkali metal salts include, but are not limited to,
salts having the formula M.sup.+ X.sup.- where M.sup.+ is a alkali metal
cation such as Li.sup.+, Na.sup.+, K.sup.+ and combinations thereof; and
X.sup.- is an anion such as Cl.sup.-, Br.sup.-, I.sup.-, ClO.sub.4.sup.-,
BF.sub.4.sup.-, PF.sub.5.sup.-, AsF.sub.6.sup.-, SbF.sub.6.sup.-, CH.sub.3
CO.sub.2.sup.-, CF.sub.3 SO.sub.3.sup.-, (CF.sub.3 O.sub.2).sub.2 N.sup.-
(CF.sub.3 SO.sub.2).sub.2 N.sup.-, (CF.sub.3 SO.sub.2).sub.3 C.sup.-, and
combinations thereof. Non-protonic organic solvents include, but are not
limited to, propylene carbonate, ethylene carbonate, diethyl carbonate,
dimethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile,
dimethoxyethane, diethoxyethane, tetrahydrofuran, and combinations
thereof.
The organic polymeric support structure may be fabricated of a
superabsorbent polymer. By superabsorbent polymer, it is meant to refer to
certain highly cross-linked polymers which absorb liquid electrolyte in
excess of 200 wt %, and preferably in excess of 300 wt %. Most preferably,
the superabsorbent polymer would absorb liquid electrolyte in excess of
500 wt %. It is essential that, upon absorption of the liquid electrolyte,
the superabsorbent polymer still appears and behaves like a solid.
Accordingly, the material cannot flow, nor can it appear wet or damp.
Further, the superabsorbent polymer support structure must not leak or
demonstrate a potential for liquid leakage, nor may it release absorbed
liquid electrolyte even under high external pressure, as may occur during
manufacturing. Characteristics of superabsorbent polymers include, but are
not necessarily limited to, high surface areas (i.e., in excess of 100
m.sup.2 /g) and high porosities (i.e., in excess of 20%). Examples of
superabsorbent polymers include, but are not limited to, those derived
from styrene and divinylbenzene, as well as from methyl (acrylates) and
polyfunctional methylacrylates.
In the instant invention, it is contemplated that the superabsorbent
polymer used in the electrolyte system 40 is a crosslinked polymer network
having certain repeating units. Repeating units are the discrete sections
of the polymer which are repeated numerous times to create the overall
polymer molecule. Specific repeating units may be selected from the group
consisting of 4,4-phenylene, 4,4'-biphenylene, 4,4"-p-terphenylene,
1,3,5-phenylene, and combinations thereof. In one preferred embodiment,
the superabsorbent polymer of the electrolyte system 40 is a
1,4-biphenylene polymeric network comprising tris(4,4'-biphenylene)
carbinol repeating units, which appear below and are referred to
hereinafter as the "4,4'-biphenylene polymer".
##STR1##
The polymeric network is made from 4,4'-dilithiobiphenyl with dimethyl
carbonate as the crosslinking agent. Methods for the fabrication of these
types of polymers are disclosed in, for example, U.S. Pat. No. 4,987,157,
to Smart, et al. Specifically commercially available, 4,4'dibromobiphenyl
is treated with t-butyl lithium, yielding 4,4'-dilithiobiphenyl. This is
then cross-linked with dimethyl carbonate.
In addition to the electrochemically active species in the polymeric
support structure, the electrolyte system 40 may further include a
material such as a binder material adapted to enhance the mechanical
integrity of the electrolyte system. This binder material may be
specifically adapted to enable the electrolyte system to be pressed into
thin films to be disposed between said positive 20 and negative 30
electrodes. The binder material may be selected from the group of
materials consisting of poly(ethylene oxide), poly(isobutylene),
poly(butyldiene), poly(vinyl alcohol), poly(ethylene), poly(propylene),
poly(vinyldene fluoride), poly(acrylonitrile), poly(dimethylsiloxane),
ethylene-propylene-diene-monomer, rubber, acrylonitrile-butyldiene rubber,
cross-linkable systems like tetra(ethylene glycol) diacrylate, and
combinations thereof. In one preferred embodiment, the binder material is
poly (ethylene oxide) or poly(isobutylene). The ratio of the binder
material to the superabsorbent polymer is between 5 wt % to 300 wt %, and
preferably from 50 wt % to 100 wt %.
The following examples are intended to illustrate the advantages of the
instant invention, and are not intended to be limitations thereof.
EXAMPLE 1
The electrolyte system described hereinabove was fabricated by providing a
superabsorbent polymer consisting of approximately 0.3 grams of
4,4'-biphenylene polymer into a mortar. To the 4,4'-biphenylene polymer,
there was added an electrochemically active material consisting of an
alkali metal salt and a non-protonic organic solvent. In this case, the
salt was LiClO.sub.4, in propylene carbonate was solvent. Specifically,
1.5 g of 1M LiClO.sub.4 in propylene carbonate was added to the 0.3 g of
4,4'-biphenylene polymer. The mixture was ground in the mortar until a
fine powder was obtained. The powder was then pressed into a film having a
thickness of approximately 0.06 cm and an area of 0.483 cm.sup.2.
Referring now to FIG. 2, there is illustrated therein the AC impedance
spectrum (at room temperature) for the electrolyte system described in
this Example 1. The AC frequency range is from 1 kHz to 100 kHz and the
measurements yield a conductivity of approximately 3.5.times.10.sup.-
.sup.3 S/cm (wherein S is a unit of conductance) This electrolyte system
offers high ionic conductivity comparable to that found in most liquid
electrolytes, and yet offers an electrolyte having solid-like properties.
EXAMPLE 2
An electrolyte system as described hereinabove was fabricated by providing
a superabsorbent polymer consisting of approximately 3.0 grams of
4,4'-biphenylene polymer into a mortar. To the 4,4'-biphenylene polymer,
there was added an electrochemically active material consisting of an
alkali salt and a non-protonic organic solvent. In this case, the salt was
LiBF.sub.4, in propylene carbonate as solvent. Specifically, 1.5 g of 1M
LiBF.sub.4 in propylene carbonate was added to the 0.3 g of
4,4'-biphenylene. The mixture was ground in the mortar until a fine powder
was obtained. The powder was pressed into a film having a thickness of
approximately 0.06 cm and an area of 0.48 cm.sup.2.
Referring now to FIG. 3, there is illustrated therein an AC impedance
spectrum for the electrolyte system according to this Example 2. Using an
AC impedance spectrum at room temperature, it was determined that the
conductivity of the electrolyte system is 1.5.times.10.sup.-3 S/cm.
EXAMPLE 3
And amount of 0.15 g of 4,4'-biphenylene polymer was provided in a mortar
to which was added 0.8 g of 1M LiBF.sub.4 in propylene carbonate. The
mixture was thoroughly ground until a fine powder was obtained.
Thereafter, 0.05 g of poly(ethylene oxide) binder material was added to
the powder mixture in the mortar and the mixture was again ground. A high
tack, high stick material was obtained. The thickness of the material was
approximately 0.06 m, and the area of the material was approximately 0.483
cm.sup.2.
Referring now to FIG. 4, there is illustrated therein an AC impedance
spectrum for the sample prepared according to this Example 3. The material
prepared accordingly to this Example 3, demonstrated a conductivity of
1.6.times.10.sup.-3 S/cm.
EXAMPLE 4
And amount of 0.15 g. of 4,4'-biphenylene polymer was provided in a mortar
to which was added a solution of 0.80 g of 1M LiBF.sub.4 in propylene
carbonate. The mixture was thoroughly ground and mixed until a fine powder
was obtained. Thereafter, 1.5 g of poly(isobutylene) solution in hexane
(0.1 g of poly(isobutylene) and in 1 g of solution) was added to the
powder and the mixture was again thoroughly ground. The resulting,
well-mixed paste was then set out so as to provide for evaporation of the
hexane. As the hexane evaporated, the paste developed a high-tack,
high-stick consistency. Thereafter, the paste was pressed at pressure of
10,000 lbs. and a rubbery thin film material was produced. A sample was
prepared from the film, that a thickness of 0.0278 cm, and an area of 1.0
cm.sup.2. Using an AC impedance spectrum at room temperature, a thin film
having a conductivity of 7.1.times.10.sup.-4 S/cm was provided. These
results are illustrated in FIG. 5.
EXAMPLE 5
And amount of 1.5 g of 4,4'- biphenylene polymer was provided in a mortar
to which was added 3.0 g of 1M LiBF.sub.4 in propylene carbonate. The
mixture was thoroughly ground and a fine powder was obtained. Thereafter,
15 g of poly(isobutylene) solution in hexane (0.1 g of poly(isobutylene)
in 1 g of solution) was added to the powder and again thoroughly ground.
The resulting well-mixed material was then set out so as that the hexane
could be evaporated. As the hexane evaporated, the paste developed a
high-tack, high stick consistency. The paste was then pressed under
pressure of 10,000 lbs. per square inch yielding a rubbery thin film with
a thickness of between 200 and 300 microns. A sample was selected from
this material having a thickness of 0.0278 cm. The area of the sample was
1 cm2. The sample was then tested by AC impedance spectrum (at room
temperature).
Referring now to FIG. 6, there is illustrated therein the AC impedance
spectrum for the sample. The AC frequency ranges from 1 hz to 100 hz.
Using this measurement, the conductivity of the sample was found to be
approximately 6.6.times.10.sup.-4 S/cm. Thereafter, a cyclic voltammagram
of the electrolyte system was run on said sample. The scan rate of the
cyclic voltammagram was 0.5 mV/s. Platinum mesh was used for both
electrodes and lithium as the reference electrode. The result of the
cyclic voltammagram is illustrated in FIG. 7. As maybe appreciated from
the perusal of the cyclic voltammagram, the stability of the electrolytes
solution described in Example 5 is quite good in the voltage range of 0.2
to 4.2 volts. No peaks were observed, demonstrating high stability of the
electrolyte system.
While the preferred embodiments of the invention have been illustrated and
described, it will be clear that the invention is not so limited. Numerous
modifications, changes, variations, substitutions and equivalents will
occur to those skilled in the art without departing from the spirit and
scope of the present invention as defined by the appended claims.
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